1. Field of the Invention
The present invention relates to a mobile telecommunication system, and more particularly to a method and an apparatus for efficiently transceiving scheduling assignment information for transmitting packet data through an uplink (UL).
2. Description of the Related Art
An asynchronous Wideband Code Division Multiple Access (hereinafter, referred to as a WCDMA) communication system employs an Enhanced Uplink Dedicated Channel (hereinafter, referred to as an EUDCH or E-DCH) in order to support a high speed packet data service through an uplink. The EUDCH is a channel proposed to improve the performance of a packet transmission in an uplink communication in an asynchronous code division multiple access communication system. The EUDCH-related technology includes new technologies for a more reduced Transmission Time Interval (TTI) together with the Adaptive Modulation and Coding (AMC) method and the Hybrid Automatic Retransmission Request (HARQ) method already used in a High Speed Downlink packet access (HSDPA). Further, a Node B control scheduling of an uplink channel is used. The Node B control scheduling for the uplink is very different from a scheduling for a downlink.
Since uplink signals transmitted from a plurality of user equipments (hereinafter, referred to as UEs) do not maintain orthogonality between the uplink signals, the uplink signals function as interference signals between themselves. Therefore, as the number of uplink signals received in the Node B increase, the number of interference signals for uplink signals transmitted from a specific UE also increases. Accordingly, as the number of the interference signals with respect to the uplink signals transmitted from the specific UE increases, the reception performance of the Node B is reduced. In order to overcome such a problem, uplink transmission power may be increased. However, an uplink signal having increased transmission power also functions as an interference signal with respect to another signal. Accordingly, the Node B limits the number of a receivable uplink signals while ensuring its own reception performance. Equation (1) represents the number of the receivable uplink signal while the reception performance of the Node B is ensured.
                    ROT        =                              I            o                                N            o                                              (        1        )            
In Equation (1), Io represents an entire reception wideband power spectral density of the Node B and No represents a thermal noise power spectral density of the Node B. Accordingly, the ROT is a radio resource capable of being assigned by the Node B for the EUDCH packet data service in an uplink.
FIGS. 1A and 1B show variations of an uplink radio resource assigned by a Node B. As shown in FIGS. 1A and 1B, the uplink radio resource assigned by the Node B is obtained by the sum of inter-cell interference (hereinafter, referred to as an ICI), voice traffic, and EUDCH packet traffic.
FIG. 1A shows variation of the total ROT when Node B scheduling is not used. Since scheduling is not performed for the EUDCH packet traffic, the total ROT grows larger than a target ROT when a plurality of UEs transmit the packet data at a high data rate at the same time. Herein, the reception performance of the uplink signal is reduced.
FIG. 1B shows variation of the total ROT when Node B scheduling is used, thereby preventing the multiple UEs from transmitting the packet data at a high data rate at the same time. That is, the Node B scheduling enables a high data rate to be permitted to a specific UE and a low data rate to be permitted to other UEs, thereby preventing the total ROT from exceeding the target ROT. Accordingly, Node B scheduling can always maintain constant reception performance.
The Node B notifies each UE of information regarding whether or not EUDCH data can be transmitted by means of a request data rate of UEs using the EUDCH or channel status information representing transmission quality of an uplink. Also, the Node B adjusts the EUDCH data rate. Further, in order to improve the performance of a mobile communication system, the Node B scheduling assigns the data rate to the UEs so that the total ROT of the Node B does not exceed the target ROT. For example, the Node B may assign a low data rate to a UE in a position remote from the Node B and a high data rate to a UE in a position near to the Node B.
FIG. 2 is a view illustrating a basic concept regarding circumstances in which a Node B scheduling is used in an EUDCH. In FIG. 2, Node B 200 supports the EUDCH and reference numerals 210, 212, 214, and 216 represent UEs transmitting the EUDCH. When a data rate of a certain UE increases, reception power received in the Node B 200 from the UE increases. Accordingly, a ROT of the UE occupies a large portion of the total ROT. In contrast, when a data rate of another UE is reduced, reception power received in the Node B 200 from another UE is reduced. Accordingly, a ROT of another UE occupies a small portion of the total ROT. The Node B 200 performs the Node B scheduling for the EUDCH packet data in consideration of the relation between the data rates and a radio resource requested by the UEs 210, 212, 214, and 216.
In FIG. 2, the UEs 210, 212, 214, and 216 transmit the packet data with different uplink transmission powers from each other according to the distance between the Node B 200 and the UEs 210, 212, 214, and 216. UE 210, in the furthest position from the Node B 200, transmits the packet data with the highest transmission power 220 of an uplink channel. In contrast, UE 214, in the nearest position to the Node B 200, transmits the packet data with the lowest transmission power 224 of an uplink channel. In order to improve the performance of a mobile communication system while maintaining the total ROT and reducing an ICI for another cell, the Node B performs scheduling so that the transmission power intensity of the uplink channel is inversely proportional to the data rate, thereby assigning a relatively lower data rate to the UE 210 having the highest transmission power of an uplink channel and a relatively higher data rate to the UE 214 having the lowest transmission power of an uplink channel.
FIG. 3 is a flow diagram illustrating a basic transmission/reception procedure between a UE 302 transmitting an EUDCH and a Node B 301 including the UE 302.
In step 303, a setup of an EUDCH is accomplished between the Node B 301 and the UE 302. The setup step includes a transmission step of messages through a dedicated transport channel. When the EUDCH setup is accomplished, the UE 302 informs the Node B 301 of scheduling information at step 304. The scheduling information may include UE transmission power information enabling uplink channel information to be understood, extra information of transmission power capable of being transmitted by a UE, and the amount of data stored in a buffer of a UE that must be transmitted.
In step 311, the Node B 301 monitors the scheduling information of the UE 302 and schedules the UE 302. When the Node B 301 determines to permit an uplink data transmission to the UE 302 in step 311, the Node B 301 transmits scheduling assignment information containing an assigned data rate and a transmission timing to the UE 302 in step 305. In step 312, the UE 302 determines a Transport Format (TF) such as a data rate for a EUDCH transmission based on the scheduling assignment information and chooses a Transport Format Resource Indicator (TFRI) indicating the TF. In step 307, the UE 302 transmits EUDCH data by means of the TFRI. Further, the TFRI, which is related information representing the TF of the EUDCH data, is transmitted to the Node B 301 in step 306 together with the EUDCH data. In step 313, the Node B 301 determines whether or not an error exists in the TFRI and the EUDCH data. As a result of the determination, when the error exists in at least one of the TFRI and the EUDCH data, the Node B 301 transmits an NACK to the UE 302 through an ACK/NACK channel, in step 308. In contrast, when any error does not exist in the TFRI and the EUDCH data, the Node B 301 transmits an ACK to the UE 302 through an ACK/NACK channel, in step 308.
The Node B 301 decides a data rate to be assigned to a UE on the basis of the scheduling information. Herein, the Node B 301 assigns a proper data rate and transmission timing to multiple UEs using an EUDCH. Further, in the scheduling, the Node B 301 assigns a resource to each UE in order to prevent a ROT value of an uplink from exceeding a target ROT value. Herein, the Node B 301 assigns many resources to a UE having a good channel condition in order to improve the entire performance of a system.
FIG. 4 is a view showing the types of data transmitted from a UE to a Node B for an uplink packet data service.
As shown in FIG. 4, a UE 400 can transmit voice and image traffic, packet data, data regarding a game, etc., to a Node B 402 through an EUDCH. The data transmitted from the UE as described above requires different quality of service (QoS) according to the types of the data. Accordingly, it is necessary to provide a method by which the Node B 402 performs a scheduling and assigns a radio resource according to quality of service required by data to be transmitted from a UE.